Apparatus and method of debarking pulp wood utilizing liquified gasses



Aug. 27, 1963 T, P, HANSQN 3,101,757

APPARATUS AND METHOD OF DEBARKING PULP WOOD UTILIZING LIQUIF'IED GASSES Filed April 24, 1961 2 Sheets-Sheet 1 A77 ORA/5) Aug. 27, 1963 T. P. HANsoN APPARATUS AND METHOD OF DEBARKING PULP WOOD UTILIZING LIQUIFIED GASSES 2 Sheets-Sheet 2 Filed April 24, 1961 United safes Patent o" 3,101,757 APPARATUS AND METHOD OF DEBARKING PULP WODD UTILIZING LIQUIFIED GASSES Thomas P. Hanson, 39 Park St., Lennoxville,

Quebec, Canada Filed Apr. 24, 1961, Ser. No. 105,079 13 Claims. (Cl. 144-311) The present invention relates to an improved method of debarking Wood and particularly pulpwood as used in the paper-making industry.

As is well known, a prime requirement of quality in the production of pulp in the paper-making industries is that the pulpwood be as completely free of bark as possible.

Accordingly, the removal of this bark is an essential and important operation and there are at present many types of apparatus available for this purpose, for example barking drums, hydraulic barkers, chain-type barkers and so on, all of which operate on the general principle that the bark is to be loosened and removed by friction, hydraulic pressure or abrasion.

It has also been established in the industry that there are certain problems involved in the barking of pulpwood which require special consideration, for example certain hardwoods are more difficult to bark than others, dry

woods are harder to -bark than wet wood, and frozen bark y is almost impossible to bark without prior treatment.

The present invention aims to provide a method of debarking wood of all types, and particularly pulpwood, which is not affected by any of the problems mentioned above and will effectively and quickly debark any type of hard or softwood, dry or wet, iirozen or unfrc-zen, leaving a clean surface wit-hout any damage to the wood itself.

This is accomplished by subjecting the wood to be debarked to a sharp freezing operation whereby the bark down to at least the outer cambium layer is frozen to a brittle glass-like state where it can 'be effectively shattered by an impact or blow clearing it from the log exterior. In accordance with a preferred means of carrying out the present invention, this is accomplished by totally immersing the Lbark-covered log in a bath of liquied gas having a temperature of say `from about 180 C. to about 200 C. for a period of from about l0 to 60 seconds, depending on the type of wood. The log with the bark sharply frozen as described is then withdrawn from the bath and subjected to a series of sharp impacts shattering the bark which breaks in glass-like particles clear of the log, leaving a smooth unblemished surf-ace.

The present invention also aims to provide an apparatus by means of which this method can be carried out continuously to provide for production debarking as is required in the paper-making industries. This apparatus consists essentially `of a main tank or enclosure adapted to -contain :a .sufficient quantity of liquied gas to permit the total immersion of logs, conveyor means adapted to convey logs into, through, and out of the liquiiied gas, and to an impact or hammer apparatus adapted to shatter the glass-like sharp frozen bark.

Having thus generally described the nature of the invention, particularly reference will be made to the accompanying drawing showing by way of illustration an apparatus by means of which the method of the invention may be carried out in a continuous cycle, and in which:

FIGURE 1 is a side elevation partially in vertical cross section of an apparatus adapted to canry out in a continuous manner the debarking method of the invention.

FIGURE 2 is a View in plan and partially in horizontal cross section of the apparatus shown in FIGURE 1.

FIGURE 3 is an enlarged detail view of the loading end of the apparatus shown in FIGURE 1.

FIGURE 4 is an enlarged detail view of the discharge end of the apparatus shown in FIGURE 1.

3,101,757 Patented Aug. 27, 1963 ICC FIGURE 5 is an enlarged detail view of the bark shattering impact hammers at the discharge end of the apparatus.

As previously mentioned, the basic concept of the present invention resides in the Adiscovery that bark when subjected to extreme cold, say for example in the neighbourhood of from about C. to about 200 C. or possibly colder, -becomes brittle and glass-like to the extent that it can be shattered clear of the wood by impact. The condition of the Wood to be barked, i.e. wet, dry, frozen, or the type of wood, i.e. hard or soft in the general terminology, does not have any bearing on the effective removal of the bark with the present method with the exception that the time of exposure to the freezing medium might be lengthened or shortened according to the type or condition.

Infact, the Worst condition of pulpwood, as considered by the prior art, namely frozen bark or Wood delivered from or resting in the woods during winter, is already partially Afrozen and therefore is, if anything, more easily treated than relatively warm, previously wet Wood looked upon as being the best for eicient barking by the previously known barking methods.

In order to provide the desired freezing action to the bark in accordance with the present method it has been found that this can be accomplished very effectively by immersing the logs in a liquiiied gas, for example any of the readily available liquifled gases, namely nitrogen, oxygen or liquid air is suitable.

As is well known, nitrogen boils at 195.8 C., air at 191 C. and oxygen at 183.0 C., all under the pressure of one atmosphere so that the logs are subjected to an intense quick freezing far beyond -anythin g encountered in nature which results in the bark down to at least the outer cambium layer `of the wood being quickly transformed to a hard glass-like consistency which will shatter into relatively small particles when subjected to a blow or impact.

In preliminary experiments using a liquified gas, air for example, and made with most types of the common woods encountered in the pulp industry, it was lfound that the time cycle of immersion, for best results on standard pulp- Wood sizes and lengths, ran from about a minimum of 10 seconds to a maximum lof about 60 seconds depending on the type of wood. Alfter immersion the Wood was withdrawn and subjected to impact as soon as possible, in from about 2 to labout 10 seconds in the experiments made. The bark Was shattered off cleanly leaving a clear undamaged rwood surface following all the contours of the log.

The time for subjecting the test logs to such impacts for maximum results ran `from about 15 seconds to about 30 seconds although with more efficient impact-producing apparatus this time could be reduced.

Examination of the test logs immediately after barking revealed that surface temperatures of the wood (after an elapsed time of about 30 seconds to 90 seconds after immersion) nan from about 0 F. to about 75 F. and that these temperatures quickly rose to approximately existing air temperatures which would indicate that the extreme freezing action apparently did not penetrate much beyond the outer cambium layer within the immersion time-s described.

It was also established that hardwoods in general required less immersion time than soft woods and, as previously mentioned, frozen logs did not require any prior treatment but were just as effectively barked as Wet or dry wood in lideal condition.

While it will be understood that the present method can be carried out by any form of apparatus providing means to contain sucient liquiiied gas to permit immersion of a log or logs and means to impart a blow or a series of blows to the frozen bark to release it from the log are provided, a preferred `form of Iapparatus suitable for production debarking is shown in the accompanying drawings.

In these drawings FIGURE 1 shows, somewhat diagrammatically, a main tank or enclosure having suitably insulated walls as indicated at 12 and including a log entrance door 14 and a log discharge door 16. A suicient quantity of liquied gas indicated at A is maintained within the tank 10 by suitable controls (not illustrated) so tha-t the liquid level indicated at B is always above the log guiding rack 18 and the lower run 19 of a continuous conveyor chain 20. The conveyor chain 20 is shown as being journalled on -suitable shafts extending through the side walls of the tank 10 with a drive pulley 22 `attached to provide a `means of driving the chain.

In the construction illustrated the logs C are fed up and into the log entrance door 14 by a ramp or chute 24 to which the logs are continuously -fed by a toothed conveyor chain 30. In view of the nature of 4the liquiied gas the entrance door 14 and discharge door 16 are each provided with 4a swinging flap or door 32 to reduce temperature losses as much as possible and subsequent vaporization of the liquied gas.

The logs D `delivered to the liquiiied gas as shown are caught by the hooks 21 of the chain 20 so as to drag them beneath the surface of the liquid gas against their natural buoyancy and through the length of the tank at a predetermined rate, dependent on the desired immersion time, and to raise them from the liquified gas and discharge them through the discharge door 32. The logs then pass down a ramp or chute 40 onto a V-shaped grate or bed 50 where they are immediately subjected to a series of rapid hammer-like impacts from opposed batteries 45, 46 of pneumatically operated reciprocating pistons 60, 62. As is shown in FIGURE 5, it is preferred that the pistons 60 are located slightly higher than the pistons 62 so that the impacts will tend to rotate the 10g D as the sharply frozen bark E is shattered thus effectively cleaning the entire circumference. As soon as the log is clean, which is accomplished in a mat-ter of seconds, the barked log is pushed clear of the grate 50 by a pneumatically operated piston 70 operating from a cylinder 72 so that the grate 50 is clear `for the next log.

As previously mentioned, the apparatus shown is illustrative only of one way in whi-ch the method of the invention may be Icarried out in a continuous cycle suitable for production debarking of pulpwood. While the logs D shown are all of approximately the same size and diameter, llogs of yany size or diameter could be debarked in a similar apparatus with provision being made by supplemental conveyor chains to ensure that they are dragged under and through the liquied gas for the desired freezing action on the bark.

I claim:

1. A method of debarking pulpwood comprising the steps of totally immersing said wood within a liquified gas for a suicient length of time to reduce the bark on said wood to a hard brittle glass-like state 4and' while in said CII state subjecting said bark to impact shattering said bark clear of said wood.

2. A method of debarking pulpwood comprising the steps of totally immersing said Wood within a liquiiied gas having a temperature of from about C. to about 200 C. `for a period of time from about l0 seconds to about 60 seconds, withdrawing said wood from said liquied gas immersion and subjecting it to impact.

3. A method of debarking pulpwood as claimed in claim 2, wherein said wood is subjected to impact within a time period of from about 2 seconds to `about 10 seconds after said liquied gas immersion.

4. A method of debarking pulpwood as claimed in claim 2, wherein the liquified gas is nitrogen.

5. A method of debarking pulpwood as claimed in claim 2, wherein the liquiiied gas is air.

6. A method of debarking pulpwood as claimed in claim 2, wherein the liquied gas is oxygen.

7. A method of debarking pulpwood llogs in a continuous cycle comprising conveying said -logs in sequence through a conned area containing a liquiiied gas while totally immersing said logs beneath the level of said liquid, removing said logs from said conned area in sequence and subjecting the outer surface of each log to a series of impacts shattering the bark therefrom.

8. A method of debarking pulpwood as claimed in claim 7, wherein said liquiied gas is nitrogen.

9. A method of continuously debarking pulpwood as claimed in claim 7, wherein said liquied gas is air.

10. A method of continuously debarking pulpwood as claimed in claim 7, wherein said liquied gas is oxygen.

11. An apparatus for the debarking of pulpwood in a continuous cycle, comprising, lan insulated container adapted to contain a quantity of liquified gas, log entry and exit ports in said container, conveyor means within said container adapted to engage and convey logs delivered within said log entry port to said log exit port through the length of said `container and beneath the surface of said liquied gas, a log-holding grate, conveyor means from said container exit port to said grate, means to impart multiple impacts to the outer surfaces of a log supported on said grate whereby the bark is shattered therefrom, and means to clear barked logs `from said grate.

12. An apparatus for the debarking of logs as claimed in claim 11, wherein the conveyor means within said container comprise endless conveyor chains provided with log-engaging hooks.

13. An apparatus for the debarking of logs as claimed in claim 11, wherein the means to impart multiple impacts to said logs comprise opposed batteries of reciprocating piston-cylinder assemblies 'and means to actuate said pistons.

References Cited in the le of this patent UNITED STATES PATENTS 1,951,084 Council Mar. 13, 1934 2,956,717 Scharf Oct. 18, 1960 FOREIGN PATENTS 125,776 Germany Dec. 4, 1901 

1. A METHOD OF DEBARKING PULPWOOD COMPRISING THE STEPS OF TOTALLY IMMERSING SAID WOOD WITHIN A LIQUIFIED GAS FOR A SUFFICIENT LENGTH OF TIME TO REDUCE THE BARK ON SAID 